1. Organic Chemistry Institute and CeNTech Westfälische Wilhelms-Universität Münster Corrensstr.40 48149 Münster Germany
2. Current address: Institute of Organic Chemistry University of Duisburg-Essen Universitätsstraße 7 45141 Essen Germany
3. Institute of Organic Chemistry Justus-Liebig University Heinrich-Buff-Ring 17 35392 Giessen Germany
4. Stanford Institute for Materials and Energy Science SLAC National Accelerator Laboratory 2575 Sand Hill Road Menlo Park CA 94025 USA